Over the last two decades, many catalytic materials have been identified as being useful for carrying out oxygenates-to-olefins (“OTO”) reactions. Nowadays, crystalline molecular sieves are the preferred catalysts because of their performance in OTO conversion and ease of large scale manufacture. Particularly preferred materials are eight-membered ring aluminosilicates, such as those having the chabazite (CHA) framework type, as well as aluminophosphates (AlPOs) and silicoaluminophosphates (SAPOs) of the CHA framework type, such as SAPO-34.
In U.S. Pat. No. 4,440,871, the synthesis of a wide variety of SAPO materials of various framework types is described, using various organic templates or structure directing agents. Also of interest are U.S. 2008-0045767, U.S. Pat. No. 7,094,389 and U.S. Pat. No. 6,984,765.
PCT/US2009/046154 discloses a method of preparing a silicoaluminophosphate molecular sieve by combining a source of phosphorus, a source of alumina, a liquid and a structure directing agent to form a synthesis mixture. This mixture is crystallized to produce a silicoaluminophosphate molecular sieve which has 90% or greater of a CHA framework type character. These sieves can be synthesized on the basis of a number of silica sources such as silica sols and colloidal silica sols.
Despite considerable research efforts in the identification of suitable catalysts for OTO applications, to date the yields for producing these catalysts, their performance and process efficiency including their use of resources has been compromised. This has impacted on the overall economic performance of OTO processes.
The present invention aims to obviate or at least mitigate the above described problems, and/or to provide improvements generally.